There is shown and described in FIG. 1 a prior art hydraulic food cutting assembly. At the heart of the hydraulic cutter is a centrifugal pump which discharges into a reducing pipe which brings the diameter of the discharge line down from a six to eight inch diameter at the pump discharge to around two inches in the discharge line. The purpose of the reducing pipe is to accelerate the food products which, for purposes of this Patent specification, shall be described in the context of uncut potatoes. The reduced diameter of the discharge line prevents the potatoes from tumbling in the line as they are directed toward the stationary cutter array or other cutter assembly. The cut food product exiting the cutter assembly and the water pass into an expansion line and ultimately into a discharge dump line. The water and the cut food product are dropped onto a conveyer chain of suitable width and length. The water drains through the conveyer chain back to a supply tank, and the cut food product is transported to an additional conveyer assembly and on for further processing. The food product, which in this example are potatoes, are dumped into the water in a supply tank which serves as a supply of water and uncut product for the centrifugal pump and a mixture of water and uncut food products pass through the suction line into the pump.
It should be apparent that while the example of food product being described in this specification are potatoes, other types of foods are also cut using similar hydraulic cutting machines to the one described herein and this invention applies equally to hydraulic cutting machines used to cut a number of different food products.
The problem is that the centrifugal pump being used is size limited in terms of the impeller and its attendant flutes have to be big enough to accept and pass through, without plugging, uncut food product that is to be pumped into the discharge line of the pump. In the case of potatoes, that means the flutes on the impeller have to be at least spaced apart approximately three to four inches so as to accept and pass through uncut potatoes. The result is that very large capacity pumps have to be employed in hydraulic cutting machines. And, since there are not a lot of hydraulic cutting machines manufactured on an annual basis, there is not enough demand for these pumps for a reputable pump manufacturer to actually try to design, if it is even possible, a pump that would meet the requirements of having a large impellor intended for continuous use in a low flow, high pressure environment.
As a result, the high capacity centrifugal pumps employed in cutting machines are typically designed for use in high capacity low lift applications such as at sewage treatment plants, commercial irrigation systems, municipal water systems, and the like. They are not designed to be used in very low volume high pressure head situations; and this is the problem since the product being cut has to be transported to the cutting assembly in a discharge line which is small enough to prevent unnecessary tumbling so that the cut food pieces are of uniform size and quality.
It has long been known that it is not necessarily the pressure that determines the ability of a hydraulic cutting system to cut food product, but rather the velocity of the food product being delivered to the cutting assembly and its array of stationary knives. As a result, hydraulic cutting assemblies are normally designed to transport the uncut food product at velocities between 20 feet per second (FPS) to 60 FPS.
In order to achieve these velocities, in the case of uncut potatoes, the discharge of the hydraulic pump, which is typically in the six to eight inch in diameter range, must be reduced to two to three inches in diameter. A reducing tube, as it is commonly called in the art, is employed to make this size reduction. It serves the dual function of reducing the diameter and also helping to align and accelerate the potatoes as they pass into the smaller discharge line. This functions just like the front half of the venturi assembly in that pressure is reduced but the speed of the fluid being pushed through the narrower discharge line is increased.
However, the pumps that have to be employed are not designed for this application. As in most cases, that high pressure portion of the pump head curve, at which these pumps are forced to operate because of the reducing tube and the dimensional constraints for the discharge line, has not even been tested by the manufactures and the pump is operating in what is commonly known as that portion of the measured pump head curve for which the pump was never intended to be used. The result of this is that the pumps take a beating and the impellers must periodically be replaced because of the erosion which occurs in an environment where there is low flow and extreme high pressure. This results in shortened pump life, and they have to be periodically replaced.
Another major problem with these low flow conditions is that in many cases the food product being pumped is not properly ejected from the impellor flutes and may be carried around inside the pump for multiple revolutions of the impellor thereby bruising or otherwise damaging the food product. Higher flows would result in less damage as the food products being pumped would be cleanly and quickly ejected from the pump.
In the prior art, the small discharge line restricts the flow to the point where the system cannot adequately accept and handle the flows required by the pump, whose size is determined the by the size of the food product to be cut.
Accordingly, what is needed is a method of increasing the flow through the pump in spite of the fact that the discharge line diameter is dictated by the size of the food product to be cut.